Acoustic emission response and fractal temporal evolution characteristics of coal body damage and failure

To address the issue that the discrete nature of acoustic emission (AE) signals and the insufficient correlation of characteristic parameters during coal body damage and failure make it difficult to reliably and comprehensively reflect the damage and failure characteristics, uniaxial loading experiments were conducted. The AE response characteristics of the coal body during damage and failure were analyzed. Additionally, based on fractal theory, the information dimension of AE signals was calculated to analyze the fractal temporal evolution characteristics of coal body damage and failure. The results showed that: ① The AE energy of the coal body exhibited distinct stage-dependent characteristics across five phases: compaction, linear elasticity, elastoplasticity, instability failure, and residual strength. A sharp increase in AE energy during the instability failure phase served as a precursor signal of macroscopic coal body fracture. This precursor signal was influenced by the initial damage level of the coal: the better the integrity of the coal, the more obvious the precursor signal during the damage and failure process. ② The coal body demonstrated prominent fractal characteristics throughout the loading process, with the information dimension decreasing as the AE signal threshold increased. At the initial loading stage, the information dimension increased due to the closure of microcracks. In the elastoplastic phase, crack propagation caused a rapid decrease in the information dimension, while in the instability failure phase, macroscopic fracture led to a subsequent increase. The stage of rapid decrease in information dimension corresponded to the critical state of internal crack propagation and coalescence, which served as an effective predictor of macroscopic coal body failure. These findings provide a theoretical foundation for the identification of precursors of coal body damage and failure and the analysis of coal failure mechanisms.